Security was tightened in Bihar’s Sheohar district Saturday, a day after Maoist guerrillas triggered a landmine blast killing six policemen ahead of the second phase of assembly elections in the state Sunday.“Combing operations were intensified. Security has been tightened to give sense of confidence among people a day ahead of polls following the Maoist strike,” Additional Director General of Police P.K. Thakur told IANS.Six policemen, including an inspector, were killed and one seriously injured Friday when they were returning to the Shyampur Bhitta police station after patrolling. The Maoists set off the mine, hidden beneath a culvert, as the police vehicle passed over it, a police official said.The state government has announced an ex-gratia of Rs.10 lakh each to the kin of those policemen killed.Sheohar, about 90 km from Patna, is one of the six districts where polling will be held Sunday in the second phase of the six-phase elections to the 243-member Bihar assembly. The district is considered to be a stronghold of Maoists.